1. Field of the Invention
The present invention belongs to the field of orthodontics. More specifically, the invention relates to a method of designing an orthodontic appliance, the said bracket being tailored to each tooth of a patient thus allowing the orthodontic appliance to be customized.
2. Description of the Related Art
Orthodontics is a medical specialty used to correct the positions of poorly positioned teeth of a dental system or when the jaw has been malformed, in order to recover a functional and aesthetic dentition.
Orthodontic treatment consists in using an orthodontic appliance to apply force to one or more teeth of a dental system/dentition so as to cause them gradually to move into a determined position in order ultimately to achieve a better tooth alignment.
The orthodontic appliance is generally formed by brackets securely fastened to the teeth and an orthodontic archwire that applies forces to the teeth via the brackets. In the current format, the orthodontic archwire is usually held in place by a housing in each of the brackets. A bracket comprises a bracket bonding pad and a bracket body comprising the housing. The bracket is attached to a surface of a tooth via the bracket bonding pad. The orthodontic archwire extends between the brackets over adjacent teeth and applies a force to each tooth in order to move the teeth individually into their determined positions.
Each bracket of the orthodontic appliance is fixed to the said bracket on a surface of the corresponding tooth which lies on the lip side, and is known as the vestibular (or sometimes labial) surface, to make it easier to attach the brackets and the orthodontic archwire and to make it easier to adjust the said orthodontic archwire.
Increasingly often, for mainly aesthetic reasons, orthodontic appliances have been developed in which each bracket is fixed to a surface of the corresponding tooth that lies inside the mouth, on the palate side, of a patient, known as the lingual surface.
One concept generally employed in orthodontics relies on configuring the orthodontic archwire as a straight archwire. What a straight archwire is, is an archwire substantially in the shape of a flat U, a semi-elliptical shape or a parabolic shape, that is to say a flat regular curve positioned with respect to the dental arch parallel to the occlusal plane.
A straight archwire is not specific to a patient's dental arch and has a simple shape that can be produced easily and on an industrial scale, and therefore at low cost.
In the case of a dental arch that requires orthodontic treatment, a preformed straight archwire that has the desired shape of the dental arch at the end of treatment is used. When a predefined straight archwire is positioned on an orthodontic appliance in position on a dental arch, the said straight archwire is partially deformed, within the elastic limits of the material of which the straight archwire is made, as they are inserted into the slot of each bracket. When the treatment is finished, the straight archwire will have returned to its initial shape because the teeth will have been moved under the effect of the forces exerted by the prestressed orthodontic archwire. In practice, a straight archwire has a rectangular, square or round cross section and its curvature is modified as the treatment progresses.
In a configuration such as this, because the orthodontic archwire is not specifically designed for a patient's dental arch, it is the brackets which are specially tailored to each one of a patient's teeth.
In order to design an orthodontic appliance tailored to each of a patient's teeth, one known method of designing and producing brackets is to produce an integral (bracket bonding pad and bracket body) bracket from numerical models of separate elements, one element representative of the bracket bonding pad and one element representative of the bracket body, and then numerically assemble them.
In order to achieve the production of a bracket, the method includes the steps of:                numerically representing the dentition of the patient,        formulating the bracket bonding pad of a bracket on the lingual face of the relevant tooth, in numerical form,        selecting a numerical representation of a bracket body from a database,        positioning the numerical representation of the selected numerical bracket body on the bracket bonding pad of the bracket.        
The bracket thus designed is a numerical object corresponding to the merger of a number of three-dimensional objects (bracket bonding pad and bracket body) designed to suit, and containing customized designs for each of the patient's teeth.
The numerical object is then exported in the form of numerical files to a machine tool or the like intended to produce the bracket from a biocompatible material in accordance with the shape thus defined.
In this method of manufacturing a bracket, only the bracket bonding pad is designed numerically from the surface of the patient's tooth, the bracket body being taken from a database and firmly attached to the bracket bonding pad later.